1 files changed, 10 insertions, 5 deletions

diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index d25603f039c..019fb626eeb 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -5635,14 +5635,13 @@ subscribed address (and not the additional To and Cc header contents)."
       (dolist (rhs
                (mm-delete-duplicates
                 (mapcar (lambda (rhs) (or (cadr (split-string rhs "@")) ""))
-                        (mapcar (lambda (domain)
-                                  (if domain
-                                      (downcase domain)
-                                    ""))
+                        (mapcar 'downcase
                                 (mapcar
                                  'cadr
                                  (mail-extract-address-components field t))))))
-        (setq ace (if (string-match "\\`[[:ascii:]]+\\'" rhs)
+        ;; Note that `rhs' will be "" if the address does not have
+        ;; the domain part, i.e., if it is a local user's address.
+        (setq ace (if (string-match "\\`[[:ascii:]]*\\'" rhs)
                       rhs
                     (downcase (idna-to-ascii rhs))))
         (when (and (not (equal rhs ace))
@@ -5664,6 +5663,12 @@ See `message-idna-encode'."
   (when message-use-idna
     (save-excursion
       (save-restriction
+        ;; `message-narrow-to-head' that recognizes only the first empty
+        ;; line as the message header separator used to be used here.
+        ;; However, since there is the "--text follows this line--" line
+        ;; normally, it failed in narrowing to the headers and potentially
+        ;; caused the IDNA encoding on lines that look like headers in
+        ;; the message body.
         (message-narrow-to-headers-or-head)
         (message-idna-to-ascii-rhs-1 "From")
         (message-idna-to-ascii-rhs-1 "To")